The present invention relates to a rubber composition and a solid golf ball. More particularly, the present invention relates to a rubber composition giving a solid golf ball good in the feeling of ball hitting, long in flight (carry) and excellent in durability, and a solid golf ball obtained therefrom.
Solid golf balls include one-piece solid golf balls integrally molded from crosslinked products of rubber compositions, and multiple-pieces solid golf balls such as two-pieces solid golf balls, three-pieces solid golf balls and four-pieces solid golf balls in which solid cores having one- to three-layers structure composed of crosslinked products of hard rubber compositions are coated with covers.
Of these solid golf balls, the multiple-pieces solid golf balls are particularly excellent in flight, so that in recent years, they have mainly been used as golf balls for playing rounds of golf. However, the multiple-pieces solid golf balls have the disadvantage that the feeling of ball hitting is hard, compared with conventional thread-wound structure golf balls. Then, it has been attempted that the cores are softened, and moreover, portions nearer to the centers of the cores are more softened to increase the deformation of the cores on hitting, thereby improving the feeling of ball hitting of the multiple-pieces solid golf balls. However, the softening of the cores deteriorates durability and resilience (carry). It has been therefore desired that multiple-pieces solid golf balls good in the feeling of ball hitting, long in flight and excellent in durability appear.
On the other hand, the one-piece solid golf balls have mainly been used as golf balls for training fields, and are liable to be cracked or chipped by repeated hitting. Accordingly, excellent durability is required so as to prevent the balls from being cracked or chipped as far as possible. Further, golf training players require that the feeling of ball hitting is also good.
Rubber compositions containing polybutadiene having a 1,4-cis bond content of 80 mol % or more, which is synthesized using a nickel catalyst or a cobalt catalyst, have hitherto suitably been used for cores of the multiple-pieces solid golf balls and core portions (solid centers) of the one-piece solid golf balls, because of their high resilience and durability. It is further known that polybutadiene synthesized using a rare earth element catalyst can be used for a similar purpose.
For example, Examined Japanese Patent Publication (Hei) 3-59931, Examined Japanese Patent Publication (Hei) 6-80123, Japanese Patent No. 2678240, Japanese Patent Laid-open Publication (Hei) 6-79018 and Japanese Patent Laid-open Publication (Hei) 11-319148 disclose that rubber compositions containing polybutadiene synthesized using rare earth element catalysts are suitable for the golf ball purpose. However, the resilience and durability of the resulting golf balls are insufficient. Further, the production workability thereof is also insufficient.
Japanese Patent Laid-open Publication (Hei) 7-268132 discloses a golf ball composed of a rubber composition mainly containing polybutadiene synthesized using a rare earth element catalyst modified with a tin compound. However, the ratio (Mw/Mn) of weight average molecular weight (Mw) to number average molecular weight (Mn) is high, so that the resilience and durability are insufficient.
Japanese Patent Laid-open Publication (Hei) 11-164912 discloses the use of modified polybutadiene rubber having a 1,4-cis bond content of 80 mol % or more, a 1,2-vinyl bond content of 2 mol % or less and a low ratio (Mw/Mn) of weight average molecular weight (Mw) to number average molecular weight (Mn) of 3.5 or less. However, this is insufficient in production workability, and there is still room for improvement in resilience and durability.
It is therefore an object of the present invention to provide a rubber composition which can give a solid golf ball improved in flight, durability and the feeling of ball hitting.
Another object of the present invention is to provide a solid golf ball improved in flight, durability and the feeling of ball hitting.
According to the present invention, there are provided the following rubber composition and solid golf ball, thereby achieving the above-mentioned objects of the present invention.
(1) A rubber composition containing (a) 50 parts to 100 parts by weight of polybutadiene rubber having a 1,4-cis bond content of 80 mol % to 100 mol % and a 1,2-vinyl bond content of 0 mol % to 2 mol %, which is modified with an alkoxysilyl group-containing compound, (b) 0 part to 50 parts by weight of diene rubber other than the above-mentioned component (a) (wherein the total amount of component (a) and component (b) is 100 parts by weight), (c) 10 parts to 50 parts by weight of a crosslinkable monomer, (d) 5 parts to 80 parts by weight of an inorganic filler and (e) 0.1 part to 10 parts by weight of an organic peroxide;
(2) The rubber composition described in the above (1), wherein modified polybutadiene rubber (a) has a ratio (Mw/Mn) of weight average molecular weight (Mw) to number average molecular weight (Mn) of 1.0 to 3.5;
(3) The rubber composition described in the above (1) or (2), wherein modified polybutadiene rubber (a) has a Mooney viscosity (ML1+4 (100xc2x0 C.)) of 30 to 100;
(4) The rubber composition described in any one of the above (1) to (3), wherein component (a) is modified polybutadiene rubber obtained by polymerizing butadiene using a rare earth element catalyst, and subsequently allowing the alkoxysilyl group-containing compound to react with the resulting polybutadiene;
(5) The rubber composition described in the above (4), wherein the rare earth element catalyst is a neodymium catalyst;
(6) The rubber composition described in any one of the above (1) to (5), wherein the alkoxysilyl group-containing compound is an alkoxysilane compound having at least one epoxy group or isocyanate group in a molecule thereof;
(7) The rubber composition described in any one of the above (1) to (6), wherein the alkoxysilyl group-containing compound is 3-glycidyloxypropyltrimethoxysilane; and
(8) A solid golf ball in which a part or the whole of a rubber substance constituting the solid golf ball is obtained by crosslinking and molding the rubber composition described in any one of the above (1) to (7).